This invention relates to cardiac rhythm management, and in particular to the implementation of systemic and methodologic time-interval (preventive-interval) blanking (or blocking) control over the ventricular pacing activity of cardiac-rhythm-management (CRM) devices.
There are many people, referred to herein as CRM subjects, or simply as subjects, who are challenged by certain compromising heart conditions that result in their being equipped, either internally (by implantation) or externally, with a cardiac-rhythm-management (CRM) device, such as a pacemaker.
CRM devices—pacemakers being good illustrations—have a commendable history of safely and confidently controlling, when necessary by the action of applying to the heart properly timed, machine-implemented (i.e., non-intrinsic), cardio-ventricular pacing pulses, cardiac-cycle rhythm in CRM subjects whose compromised heart behavior, in relation to intrinsic ventricular pacing, may be erratic, or in other ways undependable. Such devices are typically designed and programmed to apply a properly timed, non-intrinsic (what is also referred to herein as an electro-artificial) ventricular pacing pulse whenever they detect the absence in a CRM subject of a properly timed, intrinsic, ventricular pacing pulse—the important electrical pulse which functions to initiate ventricular depolarization, and which marks the beginning of the electromechanical (EM) systole in a subject's cardiac cycle. The end of the EM systole is marked by the S2 heart sound.
Generally speaking, all is normally remarkably, and comfortably, well in this realm of electro-artificial (non-intrinsic), cardio-functionality assistance until something, for some reason, causes a CRM device to deliver a non-intrinsic ventricular pacing pulse, referred to herein as an errant pulse, at the wrong time in a CRM subject's cardiac cycle, such as at the wrong moment (potentially dangerously) within, and beyond the beginning of, the electromechanical (EM) systole in the cycle, and in particular, during that part of the EM systole which contains the critical latter portion of the T-wave which portion includes what is known as the ventricular relative refractory period. An inadvertent (errant), non-intrinsic, ventricular pacing pulse delivered during this critical period—a time when ventricular cells are subject to activation—is extraordinarily dangerous.
Such an errant, non-intrinsic pulse can initiate either one of the dangerous, and often quickly fatal, heart behaviors known as ventricular fibrillation and pacemaker-mediated tachycardia, and this possibility obviously must be avoided.
The present invention—a safety-enhancing invention—relates specifically to such CRM subjects, and to the associated world of CRM ventricular pacing, and features a method and a system, based in part upon the use of heart-sound information along with other information, for preventing the potentially fatal consequence of such a device's pacing timing accidentally triggering ventricular fibrillation or pacemaker-mediated tachycardia by dangerously applying to the heart a wrongly timed, non-intrinsic ventricular pacing pulse, such as by delivering a pacing pulse during a confounding condition which may so deteriorate ECG signal information that proper timing operation of the device becomes compromised. The invention, which is computer-based, and which operates with suitable, conventionally established, algorithmic programming, accomplishes this prevention through imposing on a CRM device an appropriately time-interval-defined and established CRM control signal which, throughout the control duration time of this defined interval—referred to herein variously as a preventive interval, as a blanking interval, as a time interval determined, at least in part, in timed relation to a CRM subject's S2 heart sound, as a blanking-time duration, as a blanking interval, and as a blanking-time control duration—positively inhibits CRM ventricular-pacing activity.
While a potentially successful, imposed blanking (preventive) interval could have different, selected, overall lengths and beginning times in a cardiac cycle (as discussed hereinbelow), as long as all such intervals have lengths and time positions that fully bracket the entirety in the cycle of the ventricular relative refractory period, the preferred, and most conservatively safe practice of the present invention establishes a preventive interval that begins at ventricular depolarization onset (the beginning of the EM systole), and ends at a time which either (a) is coincident with the time of the S2 heart sound in each cardiac cycle, or (b) is at a time based upon the time of the S2 heart sound, plus or minus an optional, user determined time delta—a time addition or subtraction registered (perhaps initially and/or periodically as desired) in the computer-based system of the invention. Such a time delta, if any is deemed to be useful, is one which may be selected at any time by a medical professional who looks at an appropriate collection of subject-specific ECG waveform cycle data to decide where the associated T-wave seems regularly to exist in the subject's cardiac cycles. A T-wave which ends, for example, regularly after the associated S2 heart sound will dictate the preferred use of an appropriate “plus” time delta, whereas a T-wave which ends regularly before the associated S2 heart sound may justify the use of a “minus” time delta. The purpose of time-delta usage is to set the end of a preventive interval to occur soon after the end of the T-wave.
Regarding the time for beginning a preventive blanking interval, in accordance with practice of the present invention, other than at the most safe, and most conservative, time of ventricular depolarization onset, as just mentioned, all will be comfortably safe so long as this interval begins at any time before the ventricular relative refractory period. For examples, very good, other starting times all fall (at least some as well-recognized ECG and heart-sound fiducial markers) within the ventricular depolarization window (from and including the time of its beginning to the time of its ending), and include, representationally, the time of the peak of the R-wave, the time of the S1 heart sound, the time of the conclusion of the ventricular depolarization window, as well, optionally additionally, as selected times of specifically made, within-ventricular-depolarization-window measurements, such as measurements of intracardiac and/or intrathoracic impedance, intracardiac and/or intrathoracic pressure, blood pressure, oxygen saturation, and pulse—referred to collectively herein as other-source measurement time markers, or information. These measurement time markers and information, where made available, may so be made available for use by the system of the invention readily, and conventionally, during the ventricular depolarization window in each cardiac cycle. For example such markers and information may be made available, each where desired, as an input to signal-processing structure in the system of the invention by a CRM device to which the system is operatively connected, and which has been “instructed” to furnish such information, in each cardiac cycle, derived from conventionally provided-to-it, related input information.
Accordingly, the present invention, from a structural point of view, generally features a computer-based system for blocking, under all circumstances during the ventricular relative refractory period in each of a CRM subject's cardiac cycles, the ventricular pacing activity of an associated CRM device—the beginning and ending of such blocking in each cardiac cycle being system-defined to lie, respectively, (a) within the real-time, ventricular depolarization window in the cycle, and (b) at the time of the real-time, S2 heart-sound, plus or minus any user-defined time-delta.
In different ways, and according to user wishes, the system of the invention, which includes operatively interconnected signal-processing and control-signal-generating structures, may be wholly, or partially, integrated with a CRM subject's CRM device internal or external.
More specific structural features will be discussed below in the detailed description of the invention.
From a general methodological point of view, the invention features a signal-processing method employable in preparation for per-cardiac-cycle blanking of the ventricular pacing operation of a CRM subject's associated CRM device during a blanking time interval within each of the CRM subject's cardiac cycles, which interval always includes the ventricular relative refractory period in the cycle, this method including the steps of generating, and then making available for potential application to the CRM subject's associated CRM device, a ventricular-pacing blanking-time CRM control signal which, through appropriate method-implemented signal processing of (a) received, real-time, CRM-subject-specific, simultaneous ECG and heart-sound information, and of (b) optionally received other information including measurement time markers, has been established with a duration relating to the spaced timings of cardiac-cycle-specific ventricular depolarization and subsequent S2 heart-sound information.
Further specifics of the invention methodology are presented below herein.
These and various other features and advantages of and offered by the system and methodology of the present invention will become more fully apparent as the detailed description of it which follows is read in conjunction with the accompanying drawings.